With the development of the society and technical advancement, more and more convenient facilities, such as automobiles, motorcycles, automatic teller machines (ATM) and the like, appear in our daily life. These facilities normally need to be equipped with alarm devices against an attack, and when the facilities are subjected to the attack, the alarm devices can sense the attack and generate corresponding alarms, such as sound alarms.
At present, the alarm device normally is a shock sensor. That is, it is determined whether the facilities are subjected to the attack according to a shock signal sensed by the shock sensor. To this end, the known shock sensor is provided with a sensing device for sensing the shock signal. In the prior art, a piezo bimorph is usually used as the sensing device. The shock signal sensed by the pizeo bimorph is transmitted to a processor and is analyzed by the processor.
As is well known, the piezo bimorph is an analog element and can only sense a shock in one direction. In operation, the piezo bimorph transforms a strain thereof into an analog voltage as an output signal. Therefore, the shock signal sensed actually by the piezo bimorph may not be a real shock signal and can not describe really the attack as the real shock signal generated by the attack usually has three dimensional components. Moreover, the output signal is interfered easily by many factors, such as noise, a power supply for powering the piezo bimorph, etc.
The shock sensor also needs a complicated analog electrical circuit due to the piezo bimorph, thereby causing the shock sensor unstable.
The known shock sensor mainly executes a detection method as follows. A threshold value is predetermined, the shock signal detected by the shock sensor is compared with the threshold value, and exceeding of the threshold value indicates that the facility is subjected to the attack, thus generating a corresponding alarm. In some cases, in addition that the shock signal detected by the shock sensor is compared with a threshold value, one or more judgment conditions need to be met, in order to further decrease false alarm and missing alarm. However, as described above, the shock signal sensed by the piezo bimorph may not describe really the real attack, and therefore the false alarm and missing alarm may increase so as to cause the shock sensor ineffective.
Thus, it is desirable to provide a simple and reliable shock sensor adapted to detect the shock signal describing really the attack and thereby generate the alarm properly according to the shock signal.